Method to feed biomass tablets and logs into burners

ABSTRACT

This invention pertains to a novel new method and device to feed or inject cylindrical fuel elements (logs and tablets), made of biomass and other carbonaceous materials, into burners (furnaces, boilers, stoves or fireplaces) for use as fuel in combustion. The same method and device can also be used in gasification and liquefaction plants to feed cylindrical fuel elements as the feedstock for the gasification or liquefaction reactors. The use of such a method and device to feed biomass and other carbonaceous materials into burners and gasification/liquefaction reactors enhances the use of biomass as a resource for heating, generating electricity, and converting to gaseous or liquid fuels. Increased use of biomass, which is a renewable energy source, reduces the consumption of fossil fuel, and hence reduces detrimental environmental impacts of using fossil fuel including air pollution and global warming.

REFERENCES CITED

A. Non-Patents:

(Note: Numerals in [ ] listed below correspond to the relevantnon-patent literature discussed later this document.)

-   [1] Liu, H. and Li, Y. (2000), “Compacting Biomass and Municipal    Solid Wastes to Form an Upgraded Fuel”, Project Final Report    submitted to U.S. Department of Energy under Contract No.    DE-AC26-98FT40155, 82 pages.-   [2] Liu, H. (2000), “Economic Analysis of Compacting and    Transporting Biomass Logs for Co-Firing with Coal in Power Plants”,    Report to U.S. Department of Energy under Contract    DE-AC26-98FT40155, 52 pages.-   [3] Li, Y. and Lin, Y. (2002), “Compacting Solid Waste Materials    Generated in Missouri to Form New Products”, report to Missouri    Department of Natural Resources under Contract No. 00038-1, 90    pages.-   [4] Liu, H. and Li, Y. (2000), “Compacting Municipal Solid Waste    into Logs for Combustion at Power Plants,” Proc. of Int. Sym. on    Energy Engr., Begell House, N.Y., pp. 1420-1426.-   [5] Li, Y., Hu, R., Wenzel, J. E. and Liu, H. (2000), “Turning Yard    Waste into an Upgraded Biofuel,” Proc. of 25th Int. Tech. Conf. on    Coal Utilization & Fuel Systems., pp. 107-114.-   [6] Li, Y. and Liu, H. (1999), “High-Pressure Densification of Wood    Residues to Form an Upgraded Fuel,” Biomass and Bioenergy, Vol. 19,    No. 3, pp. 177-186.-   [7] Li, Y. and Liu, Y. (2000), “High-Pressure Binderless Compaction    of Waste Paper to Form Fuel,” Fuel Processing Technology, Vol. 67,    No. 1, pp. 11-21.-   [8] Xue, K. (1999), “Research and Design of a 5.4-Inch Diameter Mold    Rotary Press for Coal Log and Biomass Compaction”, M. S. Thesis,    Mechanical & Aerospace Engineering, University of Missouri-Columbia,    101 pages. (Advisor: Dr. Yuyi Lin).-   [9] Zhang, O. (2002), “Compacting Biomass Waste Materials for Use as    Fuel”, Ph. D. Dissertation, Department of Civil and Environmental    Engineering, University of Missouri-Columbia, 258 pages. (Adviser:    Dr. Henry Liu).-   [10] Pietsch, W. (1997), “Granulate Dry Particulate Solids by    Compaction and Retain Key Powder Particle Properties,” Chemical    Engineering Progress, April, pp. 22-47.-   [11] Pellet Fuel Institute (2004), www.pelletheat.org.-   [12] Sampson, R. and Dexbury, P. (2000), “Assessment of palletized    Biofuels”, Technical Report, Resource Efficient Agricultural    Production—Canada.

B. Patents Cited: 4325310 April 1982 Babbage 4537140 August 1985 Baker4766824 August 1988 Tenhunen 5658357 August 1997 Liu et al. 5879421March 1999 Liu et al. 5375690 April 2002 Gunnink et al. 6767375 July2004 Pearson 6814940 November 2004 Hiltunen et al. 6863878 March 2005Klepper

BACKGROUND OF THE INVENTION

1. Brief History of the Invention

This invention is closely related to, but not a direct result of, aresearch project completed in 2000 at the University ofMissouri-Columbia (UMC), under the sponsorship of the U.S. Department ofEnergy. The UMC project, entitled “Compacting Biomass and MunicipalSolid Waste to Form an Upgraded Fuel,” Investigated the feasibility ofusing high pressure to compact various types of biomass materials inorder to produce dense cylindrical-shaped objects called “biomass logs”or “biomass tablet” [1]. In this patent, the term “log” refers tocylindrical objects of a length greater than or equal to the diameter,and the term “tablet” refers to cylindrical objects of a length smallerthan the diameter. The UMC project found that by using pressure of theorder of 18,000 psi (124 Mpa), most biomass materials, including but notlimited to yard wastes (tree and bush trimmings, mowed lawn grass,fallen leaves), timber processing wastes (sawdust, tree barks, andmulches), agricultural wastes (cornstalks, corn cobs, and switch grass),and the combustible part of municipal solid wastes (waste papers,cardboard, waste wood as from discarded pallets, and discarded textileproducts) can all be compacted into biomass logs or tablets, withouthaving to use either binder or heat. More than 30 types of biomass wastematerials were successfully compacted into logs or tablets in the UMCproject [1].

The purpose of compacting biomass materials should be explained. Mostbiomass materials, such as waste papers, forestry waste, agriculturalwaste and yard waste, are very bulky (loose and fluffy) when firstcollected. They are costly to handle, store and transport, and cannot beburned efficiently in burners, boilers or furnaces. However, uponcompaction at pressure of the order of 18,000 psi, the bulk density ofthe biomass increases by 4 to 15 times [1], resulting in a densifiedfuel (logs or tablets) that is efficient to transport, handle, store andcombust. For instance, with a five times increase in density, the sametonnage of biomass material can now be transported by one instead offive trucks, and can be stored in one instead of five silos. Also, theintensity of the heat generated in any burner that uses biomass as thefuel, and the rate of chemical reaction of any reactor that uses biomassas the feedstock for gasification or liquefaction of the biomass, willgreatly increase with the increased biomass density. Another advantageof compacting biomass at high pressure is the uniformity of thegeometry, dimensions and density of the product—biomass logs. Havinguniform shape, dimensions and density also renders the biomass fuel easyto handle, package and feed automatically by using specially designedmachines.

It should be mentioned that the University of Missouri researchers ofthe biomass logs have published extensively their research findings inreports [1-3], conference proceedings [4, 5], technical journals [6, 7],and student theses [8, 9], but the University did not choose to applyfor any U.S. or foreign patent. Now that the concept of compacting andmaking biomass logs and tablets has been published for several years, itis too late for the University or anyone else to apply for a patent onthe method of producing biomass logs and tablets. However, neither theUniversity of Missouri nor anyone else has published or invented anymeans or special device to feed the biomass logs and tablets intoburners. Through unpublished work conducted by the Freight PipelineCompany, a special device to feed biomass and other carbonaceous fuellogs and tablets into burners has been invented and reduced to practice,which forms the object of this invention and patent application. In thispatent application, the terms “biomass logs” and “biomass tablets” referto biomass materials compacted or extruded into the shape of cylindersof circular or nearly circular cross sections. The term “burner” refersto any device that can burn biomass logs or tablets for any purpose—suchas a “stove”, “furnace” or “fireplace” that can burn biomass logs ortablets for heating buildings, or a “boiler” at a power plant than canburn biomass logs or tablets, with or without co-firing with coal oranother fossil fuel, for generating steam or electricity. The samedevice and method invented here for feeding biomass logs and tabletsinto burners are also applicable to feeding logs and tablets made ofother carbonaceous materials such coal or petroleum coke.

The special process to be patented here is a simple, practical and novelmethod to feed biomass and other carbonaceous tablets and logs intoburners for burning. This new feeding method will facilitate the use ofbiomass energy and bringing down the cost of such use, thereby enablingthe United States to use more biomass materials, which is a preciousrenewable energy resource largely unused and wasted at present.Increased use of biomass energy has the following benefits to thenation:

-   -   It reduces the nation's reliance on fossil fuel for heating and        generating electricity, thereby reducing air pollution and        global warming.    -   It reduces the amount of biomass waste materials that enter the        nation's landfills, thereby reducing the need for using        additional land for landfills.    -   It results in reduced use of imported oil for heating buildings,        thereby reducing the nation's reliance on imported oil.

2. Different Methods to Densify Biomass

In general, there are four different methods to densify biomass rawmaterials. They are separately discussed as follows:

Briquetting—As described by Pietsch [10], briquetting is a century-oldtechnology used mostly for agglomerating coal and charcoal fines. Itforces materials to be compacted through the gaps of two parallelrotating drums to produce pillow-shaped agglomerates called“briquettes”. A major difference between briquetting and the biomass logtechnology developed at University of Missouri is the way pressure isapplied to the material during compaction. While the latter appliespressure uniformly over the flat ends of the log or tablet (uni-axialcompaction), the former compacts on curved surfaces which make pressurenon-uniform. Consequently, the pressure applied to the rim of briquettesis much lower than that at the center of the briquettes. This makes itdifficult to form strong briquettes without using considerable amount ofbinders or heat to aid in the agglomeration. It is not uncommonly to use5 to 15% of binders to make coal briquettes. Without using binder orheat, biomass cannot be briquetted properly. In contrast, by compactingaxially from the opposite flat ends, the pressure distribution acrossany biomass log or tablet is very uniform. This enables the formation ofstrong biomass agglomerates without having to use binder or heat. Incomparison with the briquetting process, the biomass log process has thefollowing advantages: (1) It produces strong products without using heator binder; (2) it produces products in more precise and uniform shapesand density; (3) the quality of the product is more uniform and easy tocontrol; and (4) it is more suitable for making large products (largelogs and large tablets), thereby being more adaptable to mass productionat low cost.

Extrusion—Extrusion is the processing in which materials are forcedthrough a die or orifice, by using either an auger (screw), or a ram[10]. Extensive shear is generated, which together with the pressure,helps to agglomerate. While extrusion is widely used in the chemical andfood industries, it cannot be used for binderless, room-temperatureagglomeration of biomass. This is due to the fact that ordinaryextruders cannot generate the high pressure required for binderless,room-temperature compaction of biomass, which is in the neighborhood of18,000 psi [1]. Also, the extrusion process is very sensitive to thevariation of raw material properties, such as moisture and particlesize. A small variation of such material properties can often cause theextruder either to clog or to fail producing acceptable products. Incontrast, the biomass log technology was found to be able to producegood quality products (logs or tablets) without clogging or otherproblems over a rather wide range of moisture, compaction pressure andparticle size [1, 9]. This shows the superiority of the biomass logtechnology to extrusion for producing biomass logs and tablets. The onlyknown commercial use of extrusion for biomass is the fuel logs used infireplaces. Such fuel logs usually contain over 15% binder—the binderbeing either wax or an oil product. The first three of the fouradvantages cited above for biomass log process over briquetting alsohold when comparing the biomass log process with the extrusion process.

Pelletizing—Pelletizing is a processes in which materials are forcedthrough a pelletizer (pellet mill) which consists of a roller inside aperforated steel drum. The material drawn into the gap between theroller and the drum is forced through the perforations in a way similarto extrusion. Pelletizing is the most commonly used method fordensifying biomass, and sawdust is the most common material used formaking pellet fuel. However, to be successful in pelletizing, thebiomass material is usually heated to over 140 degree Celsius (284degree Fahrenheit) so that it will melt and release the lignin, whichserves as the binder. Furthermore, the perforations of the pelletizermust be small, less than about 0.5-inch (13 mm) diameter, in order toform good pellets. All these lead to high energy consumption and highcost. According to the Pellet Fuel Institute [11], an organizationrepresenting manufacturers of the pellet fuel in North America, theaverage retail price of pellet fuel in North America is approximately$150 per ton. After subtracting the cost of material collection,packaging, transportation, storage and profits by retailers, theproduction cost of the pellet fuel is in the neighborhood of $30 per ton[12]. This is considerably higher than the anticipated production costof manufacturing biomass logs as computed in the University of Missouristudy [2]: $8 per ton for 5.5-inch diameter logs, and $14 per ton for2-inch diameter logs. All the aforementioned four advantages of thebiomass log method over the briquetting method also hold when comparingwith the palletizing method.

The foregoing comparisons with competing technologies show that thebiomass log technology is superior to all the existing technologies forcompacting biomass.

Uni-axial compaction—uni-axial compaction is the method used at theUniversity of Missouri to compact biomass materials into logs andtablets. It uses a cylindrical mold and a piston of cylindrical crosssection with the piston head (i.e., the part of the piston in contactwith the biomass during compaction) slightly smaller than the innerdiameter of the mold. By using biomass feedstock of an appropriatemoisture and by using high pressure in the range of 15,000 to 20,000 psi(pounds per square inch), practically all biomass materials can becompacted into dense biomass logs or tablets without having to usebinder or heat [1]. The logs and tablets produced are dense (havingspecific gravity slightly greater than one), and they are wear-resistantand impact-resistant. They can be easily handled, transported, stored,and burned. Depending on the type of biomass materials and moisture, thebiomass logs have heating values between 7,000 and 8,500 Btu/lb. Theoptimum moisture for making biomass logs, depending on types of biomass,is 5% to 15% [1,9].

The DOE-sponsored project also conducted a detailed and rigorousinvestigation of the cost of production of biomass logs [2]. Byperforming life-cycle cost analyses, the cost of producing each ton ofbiomass logs for manufacturing facilities of various sizes (capacities)was calculated. The analysis covered two sizes of biomass logs (2-inchand 5.5-inch diameters), over the manufacturing capacity range of135,000-675,000 tons/yr. The study showed that over the plant capacityrange of 135,000 and 675,000 tons/yr., the unit cost for producing thelarge (5.5-inch-diameter) biomass logs is between $5.4 and $8.2 per ton,and the unit cost for producing the small (2-inch-diameter) biomass logsis between $12.4 and $14.2 per ton. These cost figures include not onlycapital and annual (operation and maintenance) costs but also taxes,insurance and a 15% above-inflation return-on-investment (ROI). They donot include the cost of raw material or feedstock. It was assumed thatthe biomass waste materials used for making the logs can be obtainedfree of charge because they would otherwise be headed for landfill. Tobe conservative, the avoided landfill tipping fee, usually above $30 perton, was not included in the cost analysis. Due to the inclusion of 15%ROI, the cost figures cited above are the anticipated price of the fuelthat would allow the producer to achieve above-inflation return of 15%,which is a healthy return on investment. If the producer were paid aportion of the avoided landfill tipping fee, the profit or return wouldbe much higher.

Further study by Li and Lin [3], sponsored by the Missouri Department ofNatural Resources (MDNR), showed that the biomass logs and tablets,without crushing or size reduction, burn well in stoker boilers ofordinary coal-fired power plants, and in fireplaces, furnaces, and woodstoves for heating buildings. However, the study found that at presentthere is a lack of a suitable device to feed the biomass logs andtablets into boilers, furnaces and fireplaces. Such a feeder must bedeveloped before the biomass log technology can be used widely. Thisprovided the incentive for the present invention.

3. Field of Invention

This invention deals with a method to inject or feed biomass and othercarbonaceous logs or tablets into burners (furnaces, boilers, stoves orfireplaces) for use as the fuel for combustion. It is in the generalareas of biomass and other solid fuel combustion and feeding.

4. Description of and Comparison with Prior Art

The most relevant prior art is the biomass compaction study conducted atUniversity of Missouri-Columbia [1-9]. The University researchersinvented and developed the biomass log/tablet fuel, but did not inventor develop any special equipment or method for feeding this type of fuelinto burners. Description and comparison with other related prior artsare to be given next.

There are many patented processes for producing and burning biomass andother carbonaceous fuel or fuel elements. For instance, in 1997, U.S.Pat. No. 5,658,357, entitled “Process for forming coal compact without abinder,” was issued to H. Liu et al at University of Missouri-Columbia(UMC). The patent deals with a process that applies high pressure tocoal particles inside a mold to produce water-resistant coal logs forpipeline transportation—the concept of coal log pipeline. Thiscompaction method is essentially the same used by researchers of the UMCto produce the biomass logs and tablets sponsored by the DOE projectmentioned before. The patent is different from the present patent inthat it does not deal with how the coal logs are to be combusted or fedinto burners.

Another U.S. patent (U.S. Pat. No. 5,879,421), entitled “Apparatus andmethod for forming an aggregate product from particulate material,” wasissued to H. Liu et al. in 1999. The patent deals with using specialmold shapes and back pressure during compaction to produce strong coallogs for pipeline transport. Again, it does not deal with the combustionof the coal logs or other products.

Another U.S. patent (U.S. Pat. No. 6,375,690), entitled “Process forforming coal compacts and product thereof,” was issued to B. Gunnink etal. in 2002. The process deals with heating coal-water mixture to above100 degree Celsius while the mixture is being compacted inside a mold toproduce binderless coal logs. Again, the method deals with manufacturingrather than combusting coal logs.

In July 2004, a U.S. patent (U.S. Pat. No. 6,767,375), entitled “Biomassreactor for producing gas,” was issued to L. E. Pearson. The patentdeals with an apparatus (reactor) for producing synthesis gas from abiomass feed in a closed, helical coil reactor fired by at least anatural gas fed burner. The biomass is fed into a mixing vesselpressurized by a transport gas such as natural gas which transports thebiomass feed to the reactor coil. Feeding of the biomass into the mixingvessel is through a rotary valve, which is the standard feeding methodused in pneumatic conveying of bulk solids. Such a feeding method isvery different from the feeding method described in the present patent,which rolls the biomass logs and tablets into a burner.

In November 2004, a U.S. patent (U.S. Pat. No. 6,814,940), entitled“Process for pyrolyzing carbonaceous feedstocks,” was issued to J.Hiltunen. The patent deals with a process and an apparatus forpyrolyzing (thermal conversion of) biomass and organic wastes into ahydrocarbon liquid fuel. As in the case of conventional pyrolysisprocesses, biomass or organic waste feedstock is inject into the reactorby using a screw conveyor, which is very different from the presentinvention.

In March 2005, a U.S. patent (U.S. Pat. No. 6,863,878), entitled “Methodand apparatus for producing synthesis gas from carbonaceous materials,”was issued to R. E. Klepper. The patent deals with a method andapparatus for producing synthetic gas from biomass or other carbonaceousmaterials, utilizing a controlled devolatilization reaction in which thetemperature of the feed material is maintained at less than 450 degreeFahrenheit, until most available oxygen is consumed. Two types of feedermentioned in the Claims of the patent are: a rotary feeder and a cyclonefeeder. Both are conventional devices for feeding bulk solids, and henceare very different from the log/tablet feeder in the current invention.

In April 1982, a U.S. patent (U.S. Pat. No. 4,325,310), entitled“Boilers”, was issued to T. A. Babbage. The patent deals with anautomatic boiler for combusting coal in power plants. The boiler has aninternal hopper to store and feed coal into the fire bed. Coal is storedin the hopper and fed into the fire bed in bulk form. The system wasdesigned to feed bulk solids having top size of 5/16 inch. It cannotfeed biomass logs and tablets, which are generally much greater than5/16 inch in diameter and length. Furthermore, the mechanism involved infeeding, which does not rely on the rolling of particles, is verydifferent from the one to be patented herein.

In August 1988, a U.S. patent (U.S. Pat. No. 4,766,824), entitled“Burner especially for burning biomass,” was issued to E. Tenhunen. Thepatent deals with an improvement of the stoker boiler for handlingbiomass. Feeding is done by using an automatic stoker which is forfeeding granular bulk solids (wood chips and peat) of relatively small(less than 1 inch) size, which is unsuitable for feeding biomass logsand tablets.

5. Distinct Features of Current Invention

The feeder in the current invention is different from all the knownexisting biomass and other carbonaceous material feeders for burners intwo main respects: (a) it is a special feeder designed for feeding logsor tablets (i.e., fuel or feedstock elements of circular cross section)having uniform diameter, and (b) the feeder relies on gravity to rollthe fuel elements, which is the most dependable and practical way tofeed tablets or logs of uniform or approximately uniform size. Note thatsome degree of non-uniformity in the log (tablet) diameter and length istolerated in using this feeder, as long as the logs (tablets) arecylindrical and roll easily down a slope under gravity.

BRIEF SUMMARY OF THE INVENTION

This invention deals with a method to feed or inject cylindrical fuelelements (logs and tablets), made of biomass and other carbonaceousmaterials, into burners (furnaces, stoves, boilers and fireplaces) forcombustion. The method takes advantage of the round shape and uniformgeometry of the fuel elements in the fuel feeding (injection) process.The fuel elements are stacked inside a special feeder chamber that has adownward bottom slope, and then rolled by gravity into the burner forcombustion. The feeder has a control mechanism that regulates the rateof feeding of the fuel elements into the burner. The feeder also hasone-way valves or gates that allow the biomass logs and tablets to enterthe burner, but prevent smoke and fire from entering the feeder. Due tothe use of gravity for feeding, the feeder is simple, energy-efficient,and reliable.

BRIEF DESCRIPTION OF THE DRAWINGS

As shown in FIG. 1, the device for feeding cylindrical fuel elementssuch as biomass logs or tablets consists of a feed channel in which thefuel elements are stored and subsequently released into the burner in acontrolled manner. Being cylindrical in shape, the fuel elements rollinto the burner by gravity.

FIG. 1 is a side elevation view of the biomass log or tablet feederconnected to a typical burner such as a fireplace or a woodstove. Thefeeder, shown here on the left of the burner, consists of parts 1, 2, 3,4, 5, 6 and 7. Part 1 is the inlet of the feeder for entrance of the logor tablet; part 2 (optional) is the lid to close the inlet when no logor tablet is being fed into the feeder; part 3 are the logs or tabletsin the feeder; part 4 is the inclined channel through which the logs ortablets are rolled by gravity; part 5 is the stopper, which stops themovement of the logs (tablets) in the feeder whenever the stopper isengaged, and which allows the logs (tablets) to roll/move in the feederchannel whenever the stopper is released or retrieved; part 6 are swinggates or check valves (minimum of one) to prevent fire and smoke toenter the feeder chamber; part 7 (optional) is a tube to connect thechannel from a place between the first and the last swing gate to thechimney or flue above the burner, for the purpose of venting smokes thatmay have penetrated from the burner into the feeder channel; and part 8is the outlet of the feeder system.

FIG. 2 is a cross-sectional view of the feeder channel. Normally, thewidth of the channel cross-section is only slightly longer than thelength of each fuel element, so that each channel cross-section holdsonly one element. However, in special cases when the element is short(i.e., a tablet), it may be possible to have a channel width that canaccommodate more than one tablet, such as the three tablets shown inFIG. 2. Having more than one tablet at each section increases theinjection rate, but also increases the risk of jamming to take place inthe injector. Thus, an injector that contains more than one fuel elementat each cross-section of the channel should not be contemplated unlessthis is needed for higher injection rate, and unless tests have proventhat the injector does not jam easily with more than one element at eachcross-section.

FIG. 3 gives the details of the stopper, 5, which is mounted to theinjection channel through a mounting plate 5A. The stopper is driven byan actuator, 5B, which may be a solenoid, an electric motor, a pneumaticcylinder, or a number of other things.

DETAILED DESCRIPTION OF THE INVENTION

Invented here is a method and device to inject or feed cylindrical fuelelements (logs or tablets) that are made of biomass or othercarbonaceous materials. The elements are fed into a burner, which may bea stove, boiler, furnace or fireplace, for combustion. The heatgenerated from such combustion can be utilized for producing hot water,heating buildings, producing steam, generating electricity, or otherpurposes.

The method takes advantage of the cylindrical shape and uniformdimensions of the fuel elements to be injected. It uses a speciallydesigned injector or feeder to store and inject the fuel elements.Injection is done by the force of gravity and hence is simple, reliableand convenient. The principal part of the injector is a feed channelhaving a general downward slope towards the burner. Preliminary testsconducted by the inventors indicated that the minimum slope for causingbiomass logs and tablets to roll on a metal plate or any other smoothand hard surface is about 5%, which is slightly less than 3 degrees.Thus, with a minimum channel floor slope of 3 degrees, cylindrical fuelelements inside the channel will roll down the slope by gravity andenter the burner as long as they are not blocked or physicallyrestrained from moving. The preferred vertical profile of the feedchannel is zig-zaged as shown in FIG. 1, so that maximum number of fuelelements can be accommodated in a single feeder occupying a small space.Many other arrangements are possible, such as a long straight feedchannel of uniform slope, a zig-zaged channel of non-uniform or curvedslope, and so on. However, for the fuel elements to move through thechannel by gravity unhindered, the channel must generally be inclineddownward toward the burner at a minimum average slope of 3 degrees.

Loading biomass fuel elements into the feeder is through the feederinlet, 1, as shown in FIG. 1. It is desirable but not necessary to havea lid or gate at the feeder inlet—see 2 in FIG. 1. The gate is closedwhen no logs or tablets are loaded into the feeder, and opened whenloading occurs. It is not necessary for the inlet and the lid to belocated at the end of the channel in the position as shown in FIG. 1.They may be located horizontally on the top or the bottom or verticallyon either side of the channel near the channel end, based on differentdesigns. Also, the lid may be of a variety of designs. For instance, itmay be a swing gate as shown in FIG. 1, a simple cap that can be mountedand taken out manually by hand, or other designs. It is also possible tooperate the system without having the lid, though that may not be a goodidea for it will invite insets and rodents to enter the channel.

Fuel elements, 3, are loaded inside the feeder channel, 4. The fuelelements may be made of any carbonaceous materials such as biomass,coal, petroleum coke, etc. that are compressed, extruded, or cast intocylindrical shapes of any practical diameter and length. The preferredmaterial for making the feeder channel is sheet metal such as galvanizedsteel, although other suitable metallic and non-metallic materials maybe used.

The motion and the rate of release of the fuel elements in the feederchannel are controlled by the stopper, 5, which either stops or allowsthe elements to move. The stopper can be made of various objects andshapes, and activated by various mechanisms. For instance, the stoppermay be a simple bar or a rod (see FIG. 1) controlled by a linearactuator such as a solenoid or a linear motor, with the action of theactuator controlled in turn by a PLC (programmable logic controller).Whenever a log or tablet needs to be fed into the burner, the PLCdirects the actuator which in turn pulls the bar (rod) back from the“stoppage” position to the “release” position, thereby releasing atleast one fuel element. Depending on the holding time of the releaseposition, one or more than one fuel elements can be released into theburner during each release action. In lieu of PLC, other controllersthat use a rotary switch or a microprocessor are also possible. Insteadof using a simple straight bar or rod as the stopper, it is alsopossible to use stoppers of many other designs, as for instance usingone or more than one brake shoe applied to the periphery of the fuelelements to stop their motion, in much the same manner brakes are usedon automobile wheels to stop a moving vehicle. In summary, there aremany practical ways to design and control the stopper in order toachieve desired rates of injection.

One-way valves or swing gates (part 6 in FIG. 1) are provided near thechannel outlet to prevent smoke and fire from the burner to enter thefeeder chamber. As soon as a log or tablet has passed through the firstvalve or gate, the valve or gate closes automatically, preventing smokeand fire from entering the feeder chamber upstream of the valve (gate).Use of more than one valve (gate), as shown in FIG. 1, is not necessarybut provides additional safety. The channel between valves (gates) maybe connected to the chimney or flue by a venting tube, 7. Additionalsafety measures include using a smoke detector, a fire detector, or acarbon monoxide detector mounted in the room where the burner/feedersystem is located.

Finally, the channel outlet, 8, may be simply the end of the channel, ormay have an elbow of any angle to direct the exiting fuel elements downto the burner floor or the fuel bed. The outlet may either be stationaryor mobile. A mobile outlet has an extendable arm which can reachdifferent areas of the burner, so that the fuel elements can bedistributed more uniformly in the burner. The same PLC that controls thestopper can be used to control the motion of the extendable arm. Themobile outlet is needed only for large burners where the fuel elementsexiting from the channel may not reach certain areas of the burner, orwhere the burner does not use a moving grate.

Loading of the feeder involves periodic conveying or transporting fuelelements to the feeder, either by a conveyor or manually, depending onthe size of application. For instance, for use at power plants, thequantity of fuel used is large and hence automatic conveyance of thefuel elements from the stockpile or silo to the injector is necessary.It can be done by using belt conveyors, auger conveyors, or otherautomated conveying systems. In contrast, for use in a fireplace or in aspecial stove for heating a residence or small building, the quantity ofbiomass logs or tablets used is small, and thus transporting to andloading of such fuel elements into the feeder can be done manually asneeded, such as once a day.

The invented method and device described here for feeding logs andtablets made of carbonaceous materials will greatly facilitate the useof biomass for heating and energy generation, thereby causing morebeneficial use of biomass materials, which in turn will reduce airpollution and the emission of greenhouse gases generated by using fossilfuel. Because biomass is a renewable energy resource supplied by trees,bushes and grass, whose growth converts carbon dioxide to oxygen throughphotosynthesis, use of biomass for heating and generating electricity isa carbon-dioxide-neutral process. It does not contribute to an increasein carbon dioxide in the atmosphere, and hence does not cause globalwarming. It is good for the nation and the planet earth. Although thisinvention was intended for feeding biomass fuel elements, the samemethod can be used to feed other solid fuels that are made intocylindrical-shaped elements.

1. A method and system to feed cylindrical fuel elements made ofcarbonaceous materials, including biomass, into a burner, in acontrolled manner driven primarily by gravity, using a systemcomprising: (a) a chamber that contains a straight, curved or zig-zagedchannel having a general slope towards the burner, so that the fuelelements will roll down the slope when they are not blocked orrestrained to move by a stopper, (b) an inlet of the channel for loadingthe fuel elements into the system, with the inlet being either open orcovered by a lid, (c) an outlet of the channel for releasing the fuelelements into the burner, with the outlet being either open or attachedto an elbow which helps to direct the fuel elements to an appropriateplace of the burner, (d) a stopper being a device such as a rod or abrake shoe that can either stop the motion of the fuel elements when thestopper is engaged or release the elements and allow them to roll downthe channel slope when the stopper is disengaged, (e) an actuator suchas a solenoid or electric motor that drives the stopper, (f) aprogrammable logic controller (PLC) to control the motion of theactuator, and (g) one or more check valves or swing gates mounted nearthe outlet of the channel to allow free passage of the fuel elements butto prevent smoke and fire from entering the channel.
 2. A system as setforth in claim 1 further comprising a bypass tube connected between thecheck valves near the chamber outlet and the chimney or flue of theburner, to allow smoke that entered the feed channel outlet to be ventedthrough the bypass tube for discharge into the chimney or flue.
 3. Asystem as set forth in claim 1 except that the PLC is replaced with someother control devices such as a rotary switch that can control themotion of the actuator on a cyclic basis according to preset periods orintervals.
 4. A system as set forth in claim 2 except that the PLC isreplaced with some other control devices such as a rotary switch thatcan control the motion of the actuator on a cyclic basis according topreset periods or intervals.
 5. A system as set forth in claim 1 exceptthat the burner is replaced with a reactor either for gasification orliquefaction of fuels.
 6. A system as set forth in claim 2 except thatthe burner is replaced with a reactor either for gasification orliquefaction of fuels.
 7. A system as set forth in claim 3 except thatthe burner is replaced with a reactor either for gasification orliquefaction of fuels rather than combustion purpose.
 8. A system as setforth in claim 4 except that the burner is replaced with a reactoreither for gasification or liquefaction of fuel rather than combustionpurpose.
 9. A system as set forth in claim 1 except that the outlet isattached to a mobile arm to distribute fuel elements more uniformly inthe burner,
 10. A system as set forth in claim 2 except that the outletis attached to a mobile arm to distribute fuel elements more uniformlyin the burner,
 11. A system as set forth in claim 5 except that theoutlet is attached to a mobile arm to distribute fuel elements moreuniformly in the reactor,
 12. A system as set forth in claim 6 exceptthat the outlet is attached to a mobile arm to distribute fuel elementsmore uniformly in the reactor.